The present invention relates generally to metallic nanoparticles and, more particularly, to a plasma-based method of producing uniform, spherical, metallic nanoparticles.
Metallic nanoparticles, and in particular uniform, spherical, metallic nanoparticles having a diameter of about 1-100 nanometers (nm) (see, for example, C. G. Grandqvist and R. A. Buhrman in xe2x80x9cUltrafine Metal Particlesxe2x80x9d, J. Appl. Phys. Vol. 47, no. 5, pp. 2200-2219, 1976) are important materials for applications that include semiconductor technology, magnetic storage, electronics fabrication, and catalysis. Metallic nanoparticles have been produced by gas evaporation (see K. Kimoto et al. in J. Appl. Phys. Vol. 2, p. 702, 1963; and W. Gong et al., J. Appl. Phys., vol. 69, no. 8, pp. 5119-5121); by evaporation in a flowing gas stream (see S. Iwama et al., Nanostructured Materials, vol 1, pp 113-118, 1992; and S. Panda et al., Nanostructured Materials, vol. 5, nos. 7/8, pp. 755-767, 1995); by mechanical attrition (see H. J. Fecht et al., Nanostructured Materials, vol. 1, pp. 125-130, 1992); by sputtering (see V. Haas et al., Nanostructured Materials, vol. 1, pp. 491-504, 1002); by electron beam 25 evaporation (see J. A. Eastman et al., Nanostructured Materials, vol. 2, pp. 377-382, 1993); by electron beam induced atomization of binary metal azides (see P. J. Herley et al., Nanostructured Materials, vol. 2, pp. 553-562, 1993); by expansion of metal vapor in a supersonic free jet (see K. Recknagle et al., Nanostructured Materials, vol. 4, pp. 103-111, 1994); by inverse micelle techniques (see J. P. Chen et al., Physical Review B, vol. 51, no. 17, pp. 527-532); by laser ablation (see T. Yamamoto et al., Nanostructured Materials, vol. 7, no. 3, pp. 305-312, 1996); by laser-induced breakdown of organometallic compounds (see T. Majima et al., Jpn. J. Appl. Phys., vol. 33, pp. 4759-4763, 1994); by pyrolysis of organometallic compounds (see Y. Sawada et al., Jpn. J. Appl. Phys., vol 31, pp. 3858, 1992); by microwave plasma decomposition of. organometallic compounds (see C. Chou et. al, J. Mat. Res., vol. 7, no. 8, pp. 2107-2113, 1992; and J. R. Brenner et al., Nanostructured Materials, vol. 8, no. 1, pp. 1-17, 1997, and by other methods.
Preferred methods provide a pure metallic nanoparticle product, and are to continuous, i.e. production is not halted to replenish the supply of reactants after depletion. Preferred methods, also, are cost effective, employ relatively inexpensive precursor materials, and are scalable from a laboratory scale to an industrial scale. At least some of these criteria for a preferred method pertain to some of the above methods. However, none of the above methods has been scaled up from a laboratory scale to a larger, industrial scale. Thus, cost-effective, continuous methods for producing uniform, high purity, metallic nanoparticles on a large scale remain desirable.
Therefore, an object of the present invention is to provide a method for producing uniform, high purity, metallic nanoparticles.
Another object of the present invention is to provide a continuous method for producing metallic nanoparticles.
Another object of the present invention is to provide an energy-efficient method for producing metallic nanoparticles.
Another object of the present invention is to provide a cost-effective method for producing metallic nanoparticles from inexpensive precursor materials.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
In accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention includes a method for producing metal nanoparticles. The method includes generating an aerosol having solid metal microparticles and generating a non-oxidizing plasma with a plasma hot zone at a temperature sufficiently high to vaporize the microparticles into metal vapor. The aerosol is directed into the plasma hot zone so that the microparticles vaporize, and the metal vapor is directed away from the plasma and allowed to cool, condense, and form solid metal nanoparticles.
The invention also includes metallic nanoparticles that are made by generating an aerosol having microparticles and generating a non-oxidizing plasma with a plasma hot zone at a temperature sufficiently high to vaporize the microparticles into metal vapor. The aerosol is directed into the plasma hot zone so that the microparticles vaporize, and the metal vapor is directed away from the plasma and allowed to cool, condense, and form solid metal nanoparticles.